METAL CONTAMINATION REMOVAL ON SILICON-WAFERS USING DILUTE ACIDIC SOLUTIONS

Several acids as very dilute (1:100-1:10(6)) water solutions were tested to remove metallic contaminants on silicon wafers. Total reflection x-ray fluorescence (TXRF), deep-level transient spectroscopy (DLTS), and minority carrier recombination lifetime measurements were used to evaluate the removal efficiencies. The resulting surface concentrations for iron were well below the 10(10) at/cm2 level for most solutions. The particle levels were low, comparable to an SC-1 clean. The HF solutions behaved in a different way compared to the other tested acids, HCl, HNO3, and CH3COOH, leaving a higher concentration of iron on the wafers, but a considerably lower surface recombination rate of the minority carriers in oxidized wafers. The minority carrier bulk lifetimes were in excess of 100-mu-s for the oxidized acid cleaned wafers, except to the HF cleans. Iron was found to be the dominant lifetime shortening contamination for concentrations larger than 10(11) at/cm3.